If you've ever stepped foot in a weight room, odds are you've heard those two words. Whey protein is super popular with anyone looking to build muscle, and it's frequently touted as the "the best kind of protein." If you ask someone who takes whey protein why they take it, their answer will probably be "because everyone else does."

But despite its enormous popularity, few people know what makes whey protein different from other types of protein. So, what is whey protein? If you ask your local meathead, he'll likely give you an answer heavy in "bro science." Although the production and effects of whey protein are not complicated, knowing how it's created and how it compares to other types of protein can help you make an educated decision regarding whether to take it.

What is Whey?

According to Miriam-Webster's dictionary, whey is "the watery part of milk that is separated from the coagulable part, or curd, especially in the process of making cheese, and that is rich in lactose, minerals, and vitamins and contains lactalbumin and traces of fat."

Also known as milk serum, whey is essentially the liquid that remains after milk has been curdled and strained.

Curdling milk refers to the process of separating it into solids (known as curds) and liquid (known as whey). This is done by adding either Rennet (a complex of enzymes found in the stomachs of ruminant mammals) or an edible acidic substance to the milk, or by simply letting the milk naturally go sour. The curds are used to make most types of cheese, and the whey is used to make products like ricotta cheese and whey protein supplements.

How is Whey Turned into Protein Powder or Protein Bars?

Once the whey is isolated from the curds, it is pasteurized. According to the FDA, pasteurization is a process "that kills harmful bacteria by heating milk to a specific temperature for a set period of time."

The next step involves separating the whey protein from other components in the whey. Two methods typically used to do this are ion exchange and filtration. Ion exchange uses pH adjustments to temporarily bind protein molecules to a resin. Filtration uses a series of selective filters to separate the whey into its components based on their molecule size. Both processes yield a substance with substantially higher protein than simple whey, known as whey protein concentrate.

Whey protein concentrate can be dried (often via a process called spray drying) to create a whey protein concentrate powder, or further filtered and processed to create whey protein isolate—which is any whey product with a protein content of 85 percent or greater. The protein content of whey protein concentrate can be anywhere between 25 and 89 percent. The remaining components are a mixture of fat, lactose and minerals.

Although whey protein isolate might sound like a more obvious choice than whey protein concentrate, it's often more expensive, and the extra processing can have a negative impact on some of the natural useful nutrients found in whey.

After the whey is processed into whey protein concentrate or whey protein isolate, it can then be mixed with additional ingredients and flavorings to create a wide variety of supplements, including protein powders and bars.

Why is Whey Protein so Popular?

Whey protein didn't get its good reputation for nothing. For one, it contains all nine essential amino acids, the ones our bodies cannot produce on their own, so we must get them from food. These essential amino acids are critical to repairing and rebuilding muscle and tissue, and whey protein is abundant with them.

Second, whey protein is absorbed very quickly and efficiently by the body. This is due in large part to its high presence of amino acids.

Whey protein has also been connected to several health benefits. According to the Mayo Clinic, there is "strong scientific evidence" for the use of whey protein to build muscle, and it is considered an "excellent source of protein" by experts. That benefit might not be surprising—but there's also significant evidence that whey protein can help prevent allergies, control appetite, regulate blood sugar in diabetics and aid in weight loss efforts. Additionally, a 2003 study found that whey protein can help stimulate glutathione, the antioxidant most responsible for protecting human cells.

How is Whey Protein Different from Other Proteins?

Whey protein is derived from milk. Milk contains two naturally occurring types of protein—whey protein and casein protein. Casein protein is contained in the curds of curdled milk, and it is the source of another popular type of protein powder.

One major difference between whey and casein is their absorption rate. Whey is quickly digested (for some people in as little as an hour), while casein typically takes several hours to be digested. Also, more people typically experience allergic or digestive issues with casein protein than with whey protein.

Egg protein is higher in cholesterol and has been found to be slightly less effective for satiety than whey protein. It also has less research documenting its muscle-building capabilities.

Soy protein has been found to be significantly less effective than whey protein for both building muscle and improving body composition. Rice protein has been found to improve body composition and exercise performance similar to whey protein, but it isn't a "complete protein"—meaning it doesn't contain all nine essential amino acids, as does whey protein.

Whey protein is not a magic bullet that will instantly make you stronger and healthier. That requires an overall sound approach to nutrition and a dedication to training. But it can certainly play a role in your diet if you're looking to up your protein intake in a convenient manner.

Brandon Hall
- Brandon Hall is an Assistant Content Director for STACK. He graduated from Lafayette College, where he played football and graduated with a Bachelor's degree in English.
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